18-kilo meteorite found in Antarctica

The discovery of a rock of this size is unexpected even for geologists

Geologist on the Nansen ice field with the 18-kilogram meteorite. © SAMBA Project
Read out

An international research team has found in Antarctica the largest meteorite in 25 years. The rock lay in the Nansen ice field in the eastern Antarctic - a black lump, which was still visible from 50 meters, as the polar researchers report. This is unusual, because otherwise very small meteorites are found in the South Pole region. Where it comes from is now to be determined by laboratory tests.

"This meteorite was a very unexpected find for us, not only for its weight, but also because such large meteorites are not normally found in the Antarctic, " explains Vinciane Debaille of the Université Libre de Bruxelles. Every year, you'll find around a thousand meteorites weighing less than 100 grams and maybe a hundred weighing up to a kilogram. An 18-kilo chunk is already there the exception, so the researcher.

Relic of the cosmic past

The researchers discovered the meteorite during an expedition within the framework of the SAMBA project. It organizes an expedition every year with the aim of recovering as many celestial objects as possible. "We study meteorites to better understand how the solar system formed and developed, and how Earth became such a unique planet in our system, " explains Debaille. Because the asteroids and comets flying around in our solar system are regarded as relics from the early days of our cosmic neighborhood and thus as valuable witnesses of the past.

On the remainder of our planet, the rocks and lumps of metal are quickly lost: they are overgrown by plants, disintegrate by erosion or disappear underground. That's why the mighty Antarctic ice sheets are an ideal gathering place. "On the bright ice and snow you can see the dark spots well, " said the geologist. Especially many finds were made on the Nansen Icefield, a flat area in the East Antarctic, which the researchers from the Belgian Princess Elisabeth Antarctica research station out.

No matching bag

"It was almost a bit embarrassing: Because we did not expect such a large find, we did not have a sufficiently large sample bag, " says Debaille. With bare hands or gloves, you usually do not touch a meteorite so as not to contaminate it. Fortunately, Japanese colleagues were able to help out with a suitable pouch so that the researchers could recover their find. display

Initial research has shown that the 18 kilogram chunk is a normal chondrite - a rock meteorite with numerous inclusions of silicates. Around 86 percent of all meteorites found on earth belong to this type. Its outer layer, which is formed during the flight through the earth's atmosphere, was largely worn away. "During this passage, the meteorite heats up and its outer shell melts. When it cools down, it hardens again and forms a black-brownish top layer, "explain the researchers. Therefore, one can not usually tell exactly what kind of meteorite it is. But with the new find these outer hulls were eroded, so that they could close also without gating on its type.

Thawing in the vacuum chamber

The previously frozen meteorite is now taken to a special laboratory in Japan, where it is thawed slowly under controlled conditions. "We defrost it in a vacuum to allow the ice to evaporate directly and prevent water from seeping into the rock, " explains Debaille. Only then will geologists be able to make more detailed investigations of their composition and thus deduce its age and possibly its origin.

In addition to the 18-kilo chunk, the researchers discovered during their five-week expedition 425 smaller meteorites - a total of 75 kilograms of cosmic material. At least two of these finds are most likely from the asteroid Vesta, one from Mars, they report. This can be recognized by measurements of the spectral signature of the rock, the composition of the light returned by it. "We have already discovered some so-called ecurites during the expedition, they are rather whitish and therefore easily distinguishable from other meteorites, " explains Debaille. They are rather rare and are considered as fragments of Vesta and similar asteroids.

(International Polar Foundation, 01.03.2013 - NPO)